💧 Reynolds Number Calculator

Reynolds number (Re) is a dimensionless quantity used in fluid mechanics to predict flow patterns. Re = ρvD/μ, where ρ=density, v=velocity, D=diameter, μ=dynamic viscosity.

Re > 4,000 indicates turbulent flow. Re < 2,300 indicates laminar flow. Between 2,300 and 4,000 is the transitional zone.

Laminar flow is smooth and orderly with fluid moving in parallel layers. Turbulent flow is chaotic with mixing between layers — it has higher friction losses in pipes.

At 20°C, water has a dynamic viscosity of approximately 1.002 mPa·s (millipascal-seconds). Viscosity decreases significantly as temperature increases.

Larger pipe diameter increases Reynolds number, making turbulent flow more likely at the same velocity. Smaller pipes tend to maintain laminar flow more easily.

Re determines which friction factor formula to use (Darcy-Weisbach) and whether turbulence assumptions apply. It is critical for calculating pressure drop in pipe systems.